The compound generically known as Vitamin A comprises retinol and its derivatives, also known as retinoids, in addition to its acidic or aldehyde form, respectively retinoic acid and retinal. Retinoic acid has application in the pharmaceutical and cosmetic industries being, however, prohibited in several countries for cosmetic use due to the adverse effects of irritability which it may cause. Examples of pharmaceutical applications of retinoic acid can be found in the article “Relationships between structure and activity of retinoids”, published by Nature, Volume 236, pages 110–113, of Sep. 9, 1996.
In the cosmetic area Vitamin A is usually employed in the form of retinol or some of its retinoids such as retinyl palmitate, and the use of retinol causes various biologic activities, many of which are highly desirable in cosmetic compositions, particularly in those intended to improve the general conditions of the skin of the individual subjected to the topic use thereof. Results achieved by the topic use of Vitamin A are described in passages contained in pages 82–119 of the article entitled “Vitamin A Complex”, written by Wade Cheng, PhD and Shirley DePetris and published by Skin Inc., March/April 1998.
Moreover, regulation and balance of the epidermal cellular growth through the total synthesis of collagen, among others, such as retention of water in the skin, are also known as effects resulting from the use of Vitamin A in its pure form, called Retinol.
One problem resulting from the use of Vitamin A, either in its pure form or as a derivative, is that, on the one side it promotes the effects of increasing the cellular activity at the level of the dermis and epidermis, accelerating the process of proliferation and differentiation of the keratinocytes and reorganization of the fibers of the dermis (collagen and elastin). But on the other side it must be administered at low doses due to its toxicity. This fact limits the use of Vitamin A and its derivatives to lower contents or requires the utilization of other means that are able to minimize the discomfort of irritation in the skin.
In fact, the use of retinol at low contents is quite common, as shown by several studies, such as the one conducted by the Hamburg Clinic of Experimental Dermatology, in Germany, which doscloses tests with low contents of Retinol (0.034%) for men and women with age between 22 and 34 years and which show that such a concentration of retinol could reduce the amount and the deepness of wrinkles. Therefore, this study generically shows the effect of reducing wrinkles by the use of low contents of retinol.
On the other hand, what has been observed is that, even though low concentrations of retinol effectively cause little or no irritation, the results on the skin can remain below the desired levels for the present standards of demand of the consumers in view of the small amount of retinol incorporated in the cosmetic composition and available for its biological action.
In this respect, there have been attempts to obtain compositions of Vitamin A that present effective action and do not cause adverse effects, for instance, the irritation of the skin. As an example, documents U.S. Pat. No. 5,516,793 and U.S. Pat. No. 5,703,122 in the name of Avon Products, Inc., are incorporated herein as prior art references. These documents describe a generic association of amounts ranging from 0.5 to 25% by weight of Vitamin C with several irritating active principles, among which Vitamin A is included. This association, however, has the exclusive purpose of reducing irritation of the skin caused by Vitamin A.
It is therefore an objective of the present invention to provide an alternative for the use of Vitamin A at such concentrations that enable an increase in its properties which are beneficial to the skin, without presenting the problems cited above.